Relay and cross-connect

ABSTRACT

The present invention relates to a fuse-relay including a first pole ( 1, 11, 21, 31, 81 ) and a second pole ( 2, 12, 22, 32, 82 ). According to the invention the fuse-relay includes a resilient device ( 5, 18, 27, 37, 87 ) that is held in an elastically deformed position by a fuse ( 6, 16, 26, 36, 86 ) when the fuse ( 6, 16, 26, 36, 86 ) is whole; and in that the resilient device ( 5, 18, 27, 37, 87 ) is arranged to make or break a connection between the first pole ( 1, 11, 21, 31, 81 ) and the second pole ( 2, 12, 22, 32, 82 ) when the fuse ( 6, 16, 26, 36, 86 ) is blown. The invention also relates to a cross-connect with such fuse-relays, to a telecommunication system with such cross-connects and to a connection method.

TECHNICAL FIELD

The present invention relates to a relay, to a cross-connect and to amethod for connecting xDSL modems and similar.

BACKGROUND OF THE INVENTION

Digital Subscriber Line (DSL) is a technology that dramaticallyincreases the digital capacity of ordinary telephone lines into a homeor office. The different versions of DSL include for example ADSL(Asymmetrical DSL), HDSL (High bit rate DSL) and VDSL (Very high bitrate DSL), which are commonly denoted as xDSL.

Now, not all subscribers may want to have xDSL, therefore in somesubscriber line equipment, the total number of subscriber lines arehigher than the number of xDSL modems. When a new subscriber order axDSL subscription, then a manual installation procedure is required,wherein an unused xDSL modem is connected to the subscriber's line. Thisis a costly operation.

A way of reducing the manual intervention is to use a cross-connect inthe form of a switch-matrix or similar. This is done in e.g. U.S. Pat.No. 5,905,781 wherein mechanical or electrical relays are used, WO01/45431 wherein mechanical or solid-state relays are used, and U.S.Pat. No. 6,262,991 wherein switches are mentioned. The switches/relaysare then digitally controlled to enable a subscriber to be connected toone of the xDSL modems.

SUMMARY OF THE INVENTION

The problem with existing solutions of cross-connects is that the totalnumber of relays will be quite high and relays are expensive, quitelarge and often consume a lot of power.

The purpose of the present invention is to solve this problem by using anew type of relay. An intelligent part of the invention is to realisethat in most cases it is only necessary to connect a subscriber'sterminal to a modem, but seldom to disconnect. Thus, a simple type ofrelay can be used, which is described in claim 1.

The advantages are that such a relay is simple, small and cheap, whichalso makes the cross-connect cheap and connections may be made remotelyin a simple way. Further advantages will follow from the differentembodiments.

The invention will now be described in closer detail with the aid ofpreferred embodiments and with reference to enclosed drawings.

DESCRIPTION OF THE FIGURES

FIG. 1 shows a communication system with xDSL modems

FIG. 2 shows an embodiment of a communication system according to theinvention with xDSL modems and a cross-connect according to theinvention

FIG. 3 shows an embodiment of a communication system according to theinvention with xDSL modems and two cross-connects according to theinvention

FIG. 4 shows an embodiment of a communication system according to theinvention with xDSL modems and two cross-connects according to theinvention

FIGS. 5 a and b shows a first embodiment of a fuse-relay of a makecontact type according to the invention

FIGS. 6 a and b shows a second embodiment of a fuse-relay of a makecontact type according to the invention

FIGS. 7 a and b shows a third embodiment of a fuse-relay of a makecontact type according to the invention

FIGS. 8 a and b shows a fourth embodiment of a fuse-relay of a makecontact type according to the invention

FIGS. 9 a and b shows a fifth embodiment of a fuse-relay of a makecontact type according to the invention

FIGS. 10 a and b shows a first embodiment of a fuse-relay of a breakcontact type according to the invention

FIGS. 11 a and b shows a second embodiment of a fuse-relay of a breakcontact type according to the invention

FIGS. 12 a and b shows a third embodiment of a fuse-relay of a breakcontact type according to the invention

FIGS. 13 a and b shows a fourth embodiment of a fuse-relay of a breakcontact type according to the invention

FIGS. 14 a and b shows a first embodiment of a fuse-relay of achange-over type according to the invention

FIGS. 15 a and b shows a second embodiment of a fuse-relay of achange-over type according to the invention

FIGS. 16 a and b shows a third embodiment of a fuse-relay of achange-over type according to the invention

FIGS. 17 a and b shows a fourth embodiment of a fuse-relay of achange-over type according to the invention

FIGS. 18 a, b and c shows an embodiment of a fuse-relay with indicatorand test button

FIGS. 19 a and b shows a first embodiment of a cross-connect accordingto the invention

FIG. 19 c shows a second embodiment of the switch part of across-connect according to the invention

FIG. 19 d shows a third embodiment of the switch part of a cross-connectaccording to the invention

FIG. 20 shows a practical implementation of a cross-connect according tothe invention

FIG. 21 a shows a method for reducing the number of relays in across-connect according to the invention

FIG. 22 shows a third embodiment of a cross-connect according to theinvention

PREFERRED EMBODIMENTS

FIG. 1 shows a simplified view of a telecommunication system.Subscribers' terminals 101 are connected to splitter filters 102. Thelow pass sides of the splitter filters 102 are connected to line cards103, providing PSTN services, and the high pass sides of the splitterfilters are connected to xDSL modems 104, providing xDSL services.

Since not all subscribers want xDSL services it would be a waste toinstall one modem per subscriber. In FIG. 2 is shown according to theinvention a way to have a few xDSL filters 104 that easily can beconnected to the subscribers' terminals 101. A cross-connect 105 isplaced between the splitter filter 102 and the xDSL modems and has theability to connect any of subscriber's user terminals 101 with any ofthe xDSL modems 104. The cross-connect 105 will be described in moredetail below.

An alternative solution is shown in FIG. 3. If there is a wish to sparealso splitter filters then two cross-connects, 106, 107, one on eachside of the splitter filters 105 can be used. Further, separate relays108 are provided. In the basic case for a subscriber, the relay 108 isclosed and thus provides connection between the subscriber's terminal101 and his line card 103. If the subscriber wants to have xDSL, thenthe relay 108 is opened, while other relays within the cross-connects106, 107 are closed. In this way a connection is provided from thesubscriber's terminal 101 to the line card over the splitter filter 105and thus access to the xDSL modem 104 will also be obtained.

A further alternative is shown in FIG. 4. It is like FIG. 3, but noseparate relay is needed because two cross-connects 116, 117 areprovided which include change-over relays. The changeover relays arearranged so that in the basic case they provide connection between thesubscriber's terminal 101 and his line card 103 directly over a line110. If the subscriber wants to have xDSL, then the relay 108 is changedso that the old connection is broken and a new connection is madetowards to splitter filter 105 instead. Thus a connection is providedfrom the subscriber's terminal 101 to the line card over the splitterfilter 105, like in FIG. 3, and thus access to the xDSL modem 104 willalso be obtained.

There are also other alternatives on where and how to connect thecross-connect and the exact placement is of no relevance for the presentinvention.

A cross-connect may look in different ways. A preferred embodiment isfor the cross-connect to include a switch-matrix with relays. FIGS. 5 aand b shows a new type of fuse-relay, which includes a first pole 1, asecond pole 2 and a third pole 3. A fuse 6 is connected between thesecond pole 2 and the third pole 3. A switch 5 is connected between thefirst pole 1 and the second pole 2. Said switch 5 can be influenced bythe fuse 6 to be either in an open or a closed position.

The simplest switch 5 is some sort of resilient device, such as aspring. In FIGS. 5 a and b the resilient device is a blade spring orsimilar that is positioned in a bent and thus elastically deformedposition, thus possessing elastical deformation energy. If in FIG. 5 a asufficiently high current is sent between the second pole 2 and thethird pole 3 the fuse 6 will blow and thus the blade spring 5 will bereleased. The result will then be FIG. 5 b, in which the first pole 1and the second pole 2 now will be connected.

In many cases, it would be much more advantageous to separate the fuseand the switch totally. Examples of a four-pole fuse relay are disclosedin FIGS. 6 a and b, 7 a and b, 8 a and b and 9 a and b. There is in someway a switch 15, 25, 35, 85 between a first pole 11, 21, 31, 81 and asecond pole 12, 22, 32, 82. A fuse 16, 26, 36, 86 is connected between athird pole 13, 23, 33, 86 and a fourth pole 14, 24, 34, 84. This makesit possible to transmit a sufficiently high current between the thirdpole 13, 23, 33, 83 and the fourth pole 14, 24, 34, 84 in order to blowthe fuse 16, 26, 36, 86 without affecting anything connected to thefirst pole 11, 21, 31, 81 or the second pole 12, 22, 32, 42. Further,some sort of resilient device, spring, is connected to the third pole13, 23, 33, 43 and is held in an elastically deformed position by thefuse 16, 26, 36, 86, thus binding energy. When the fuse 16, 26, 36, 86is blown the spring will be released and will cause the connection ofthe first pole 11, 21, 31, 86 with the second pole 12, 22, 32, 82.

In FIGS. 6 a and b the relay includes a first metal blade 10 connectedto the first pole 11, a second metal blade 17, connected to the secondpole 12, a third metal blade 18 connected to the third pole 13, a fourthmetal blade 20 connected to the fourth pole 14 and an insulator 19somewhere between the second metal blade 17 and the third metal blade18, preventing the second metal blade 17 and the third metal blade 18 tocome into electrical contact. When the fuse 16 is whole, then the thirdmetal blade 18—acting as a blade spring—is in a bent, i.e. elasticallydeformed, position as in FIG. 6 a. But if the fuse 16 is blown, see FIG.6 b, then the third metal blade 18 will be released and will instead,via the insulator 19, press the second metal blade into electricalcontact with the first metal blade. Thus, the first pole 11 and thesecond pole 12 will now be in electrical contact.

In FIGS. 7 a and b and 8 a and b the relay includes a coil spring 27, 37with a switch contact 28, 38. The spring is held in an elasticallydeformed position—either compressed, FIG. 7 a, or stretched, FIG. 8a—with the aid of the fuse 26, 36. There is electrical contact betweenthe fuse 26, 36 and the spring 27, 37, so that a current can flowbetween the third pole 23, 33 and the fourth pole 24, 34 in order toblow the fuse 26, 36. However, both the fuse 26, 36 and the spring 27,37 are insulated from the switch contact 28, 38 by means of some kind ofinsulation 29, 39.

When the fuse is blown, see FIGS. 7 b and 8 b, the spring 27, 37 will bereleased and the switch contact 28, 38 will be pressed against the firstpole 21, 31 and the second pole 22, 32 to make electrical contactbetween the first pole 21, 31 and the second pole 22, 32.

In FIGS. 9 a and 9 b the relay includes a torsion spring 87 with aswitch contact 88. The spring is held in an elastically deformedposition with the aid of the fuse 86—i.e. the upper end 110 of thespring is twisted around the axis of the spring, while the lower end 83is not. There is electrical contact between the fuse 86 and the spring87, so that a current can flow between the third pole 83 and the fourthpole 84 in order to blow the fuse 86. However, both the fuse 86 and thespring 87 are insulated from the switch contact 88 by means of some kindof insulation 89.

When the fuse is blown, see FIG. 9 b, the spring 87 will be released andthe switch contact 88 will be pressed against the first pole 81 and thesecond pole 82 to make electrical contact between the first pole 81 andthe second pole 82.

In FIGS. 10 a and b, 11 a and b, 12 a and b and 13 a and b the relays ofmake contact type in FIGS. 6 a and b, 7 a and b, 8 a and b and 9 a andb, respectively, are modified into relays of break contact type, whichmeans that the first pole and the second pole will work differentlycompared to the earlier Figures.

In FIGS. 10 a and b, the first pole 42 is connected to a first metalblade 43 placed in such a way that when the fuse 16 is whole there willbe a connection between the second metal blade 17 and the first metalblade 43 and thus between the second pole 12 and the first pole 41.Thus, the second metal blade 17 and/or the first metal blade 43 is/arepreferably in an elastically deformed position, i.e. somewhat bent, toensure good contact.

When the fuse 16 is blown, see FIG. 10 b, then the third metal blade 18will be released and the second metal blade 17 will be moved asdescribed in connection with FIGS. 6 a and b. This means that theconnection between the second pole 12 and the first pole 41 will bebroken.

In FIGS. 11 a and b, FIGS. 12 a and b and FIGS. 13 a and b the switchcontact 28, 38, 88 makes connection between the second pole 51, 61, 91and the first pole 52, 62, 92 when the fuse 26, 36, 88 is whole.However, see FIGS. 11 b, 12 b and 13 b, when the fuse 26, 36, 96 isblown, then the spring 27, 37, 87 will be released and moved asdescribed in connection with FIGS. 7 a and b, 8 a and b and 9 a and b,respectively, and thus said connection will be broken. In FIGS. 11 a andb, FIGS. 12 a and b and FIGS. 13 a and b the fuse 26, 36, 86 will alonehold the switch contact to make contact between the first pole 52, 62,92 and the second pole 51, 61, 91. Preferably, thus, the fuse 26, 36, 86should be resiliently suspended, so as to press the switch contact intoplace.

In FIGS. 14 a and b, 15 a and b, 16 a and b and 17 a and b the relays ofmake contact type in FIGS. 6 a and b, 7 a and b, 8 a and b and 9 a andb, respectively, and the relays of break contact type in FIGS. 10 a andb, 11 a and b, 12 a and b and 13 a and b, respectively are combined intochange-over-relays of the type break-before-make. In the FIGS. 14 a andb, 15 a and b, 16 a and b and 17 a and b the first pole from FIGS. 10 aand b, 11 a and b, 12 a and b and 13 a and b will now be called thefifth pole.

In FIGS. 14 a and b, a fifth pole 41 is connected to a fifth metal blade42 placed between the second metal blade 17 and the third metal blade 18in such a way that when the fuse 16 is whole there will be a connectionbetween the second metal blade 17 and the fifth metal blade 42 and thusbetween the second pole 12 and the fifth pole 41. When the fuse 16 isblown, see FIG. 14 b, then the third metal blade 18 will be released andthe second metal blade 17 will be moved as described in connection withFIGS. 6 a and b. This means that the connection between the second pole12 and the fifth pole 41 will be broken and instead there will be aconnection between the second pole 12 and the first pole 11.

In FIGS. 15 a and b, 16 a and b and FIGS. 17 a and b the second pole 22,32, 82 has an additional connection point 51, 61, 91 to which the switchcontact 28, 38, 88 makes connection when the fuse 26, 36, 86 is whole.Further, the switch contact 28, 38, 88 also makes connection to thefifth pole 52, 62, 82 when the fuse 26, 36, 86 is whole. Thus, when thefuse 26, 36, 86 is whole, the second pole 22, 32, 82 is connected withthe fifth pole 52, 62, 82. However, see FIGS. 15 b, 16 b and 17 b, whenthe fuse 26, 36, 86 is blown, said connection will be lost and insteadthe first pole 21, 31, 81 and the second pole 22, 32, 82 will beconnected, as described in connection to FIGS. 7 a and b, 8 a and b and9 a and b, respectively.

These are some examples on how a fuse-relay may look. The skilled man inthe art will vary the fuse-relay in numerous ways without departing fromthe main idea.

The fuse-relay described above is a one-shot switch and once the fusehas been blown the connection cannot be rebroken/remade except forreplacing the fuse with a new fuse or by replacing the fuse-relay with afuse-relay with a whole fuse. A fuse-relay may be put in a small packagepossible to put in a socket for easy replacement. The fuse-relay mayalso be provided with an indicator indicating if the relay is “on” or“off”. Further, the fuse-relay may be provided with a test-button orsimilar in order to test connections without blowing the fuse.

In FIGS. 18 a and 18 b is shown an example on how to implement anindicator. FIG. 18 a corresponds to FIG. 6 a and FIG. 18 b correspondsto FIG. 6 b, however drawn three-dimensional. Further, an indicator 71is added on top of the fourth metal blade 20. The fourth metal blade 20is also held in a bent, i.e. elastically deformed, position by the fuse16 and thus works as a blade spring. When the fuse 16 is blown, see FIG.8 b, then the fourth metal blade 20 will be released and the indicator71 will be seen in a window 73 or similar.

That was a mechanical solution on how to indicate. Of course it is alsopossible to find electrical solutions, such as to test the connection bytransmitting a weak current between the third pole and the fourth poleand to see if there is a connection or not, i.e. to see if the fuse iswhole or not, e.g. by making a circuit light a light emitting diode. Thecurrent should of course then not be so strong as to blow the fuse.

In FIG. 18 a is also indicated a test button 74. When the test button 74is pressed, see FIG. 18 c, an electrical contact will temporarily becreated between the first pole 11 and the second pole 12, without havingto blow the fuse 16. Thus, the connection may be tested.

A cross-connect can be made using the fuse-relays described above, e.g.by making a switch-matrix as shown in FIG. 19 a, showing simplified thefuse part of the switch matrix and 19 b, showing simplified the relaypart of the switch matrix.

The fuse part of the switch matrix is built up from addressing rows 121and addressing columns 122 and with a fuse 123 connected in eachcross-point of the addressing rows 121 and addressing columns 122. InFIG. 19 a the fuses 123 are drawn schematically as if directly connectedbetween the addressing rows 121 and addressing columns 122. Inpractise—compare FIGS. 6 to 17—the third pole of the fuse-relay will beconnected to the addressing row 121 and the fourth pole will beconnected to the addressing column 122 or vice versa.

Addressing of a certain fuse-relay—in order to blow its fuse to make aconnection—can be made by selecting one addressing row 121 and oneaddressing column 122 and transmitting a sufficiently high currentthrough said addressing row 121 and addressing column 122. An example onhow this can be done is shown in FIG. 19 a. For each addressing row 121,a transistor 124 is connected with its emitter to said addressing row121, with its collector connected to a power source and with its baseconnected to a row demultiplexor 127. For each addressing column 122, atransistor 126 is connected with its collector to said addressing column122, with its emitter connected to ground and with its base connected toa column demultiplexor 127. Naturally, it will work equally well if theconnections for the addressing rows and addressing columns areinterchanged. The row demultiplexor 125 and the column demultiplexor 127have inputs to receive a row address RA and a column address CA,respectively, from a control unit 128 or similar. The demultiplexorsfurther have inputs for enable signals E.

The switch part of the matrix in FIG. 19 b includes in a correspondingway switching rows 131 and switching columns 132 with switches 133connected between them, i.e.—compare FIGS. 6 to 17—the first pole of afuse-relay is connected to a switching row 131 and the second pole of afuse-relay is connected to a switching column 132 or vice versa.

When the change-over fuse-relays in FIGS. 14 to 17 are used, there willbe additional switching rows 141, see FIG. 19 d.

In order to use the cross-connect for connecting xDSL modems, compareFIGS. 2 and 19, a cross-connect 105 with fuse-relays of make contacttype, compare also FIGS. 5 to 9, can now be connected with the switchingrows 131 connected towards the subscribers' terminals and with theswitching columns 132 connected towards the xDSL modems 104. Intelecommunication each subscriber line will include two wires, whichmeans that the fuse-relays should be dual fuse-relays, i.e. with oneswitch per wire working simultaneously.

In FIG. 3, the switching rows 131 will be connected towards thesubscribers' terminals 101 and the line cards 103, respectively, and theswitching columns 132 will be connected towards the splitter filters105. Also here fuse-relays of make contact type will be used, compareFIGS. 5 to 9, but additionally also fuse-relays of break contact typefor the separate relays 108.

In FIG. 4, cross-connects 116, 117 with change-over fuse relays, will beused, compare FIGS. 14 to 17 and FIG. 19 d and the additional switchingcolumns 131 of the first cross-connects 116 will be connected to theadditional switching columns in the second cross-connect 117.

Connecting an xDSL modem can be made remotely, by addressing anaddressing row 121 and column 122 and enabling the addressing with anenable signal E. Then a current will flow in said addressing row 121 andcolumn 122, whereupon the corresponding fuse 123 will blow. Consequentlythe corresponding switching row 131 and column 132 will be connected,thereby connecting the subscriber's terminal with the selected xDSLmodem. If the fuse-relay is provided with an indicator, then saidindicator will now indicate that a connection with the xDSL modem hasbeen made.

Preferably, there will be in the switch control unit some type of checkin the addressing of the modem, so as to prevent selection of a modemwhich is already selected.

In FIG. 20 is shown a practical example of a cross-connect with manyfuse-relays 161. The cross-connect is arranged like a book, and isdivided in several “pages” 162, with the rear sides 163 of the “pages”mounted on a back 164 with “hinges” or other similar means, so that the“pages” 162 are movable like the pages in a book. This facilitateschanging of a fuse-relay 161, when necessary.

To facilitate the finding of the fuse-relay that is to be changed, lightemitting diodes 165, 166 can be used. If it is previously selectedsomewhere which fuse-relay is to be changed, then the row with saidfuse-relay may be indicated with a row light emitting diode 165 and thecolumn with said fuse-relay may be indicated with a column lightemitting diode 166. This method of indicating may of course also beemployed if the cross-connect is not in the form of a book.

A full “all to all” switch matrix will require N_(C)·N_(M) number ofrelays, where N_(C) is the number of subscriber lines and N_(M) is thenumber of modems. It is, however, possible to reduce the number ofrelays if a small probability of “no unused modem available” is allowed.If, in a very large switch matrix, e.g. 10% of the subscribers want tobe connected to xDSL and if the modems corresponds to 20% of allsubscribers, then it is enough if each subscriber can be connected toabout 5 to 10 modems. This corresponds to 5–10 relays per subscriber. Inthis case it is possible to automatically connect a new subscriber in99% of the cases. In the rest of the cases manual connection isnecessary.

If a clever algorithm is used when selecting modem, then the statisticscan be improved even further. When selecting a modem, the modem shouldbe selected where the rest of the subscribers able to connect to saidmodem, either already are connected to another modem, or have thehighest possibilities to connect to other modems.

In FIGS. 21 a and b is shown an example with five subscribers S1, S2,S3, S4, S5 and three modems M1, M2, M3. For a full connection, see FIG.21 a, each subscriber should have had connection possibilities with allthree modems making it 5·3=15 connection possibilities. However, in FIG.21 b, as an example, it is chosen that each subscriber has only twoconnection possibilities in a way that the first subscriber S1 canselect the first modem M1 or the second modem M2, the second subscriberS2 can select the first modem M1 or the third modem M3, the thirdsubscriber S3 can select the second modem M2 or the third modem M3, thefourth subscriber S4 can select the first modem M1 or the third modemM3, the fifth subscriber MS5 can select the second modem M2 or the thirdmodem M3.

Let us say that the first subscriber S1 wants to be connected to amodem. There is the choice between the first modem M1, to which threeother subscribers S2, S4, S5 have the possibility to be connected, andthe second modem M2, to which three other subscribers S3, S4, S6 havethe possibility to be connected, counting only the subscribers who arenot already connected to a modem. Looking at the subscribers S2, S4, S5with the possibility to be connected to the first modem M1; each of themhas a possibility to be connected to two modems. The same situationoccurs at the second modem M2. Further, there are equally manyconnection possibilities to the first modem M1 as to the second modemM2. Thus, any of the modems M1, M2 can be selected. Let us select toconnect the first subscriber S1 to the first modem M1.

Now the first modem M1 is occupied, meaning that some subscribers S2,S4, S5 only have one choice of modem, e.g. if the second subscriber S2wants to be connected to a modem, it is only possible to select thethird modem M3. However, let us say it is the third subscriber S3 thatwants to be connected to a modem. The third subscriber has the choicebetween the second modem M2, to which two other subscribers S4, S6 havethe possibility to be connected (not counting the first subscriber S1,who is already connected to a modem), and the third modem M3, to whichthree other subscribers S2, S5, S6 have the possibility to be connected.Looking at the subscribers S4, S6 with the possibility to be connectedto the second modem M2; the fourth subscriber S4 can only select thesecond modem M2, while the sixth subscriber S6 also can select the thirdmodem M3. Looking at the subscribers S2, S5, S6 with the possibility tobe connected to the third modem M3; the second subscriber S2 and thefifth subscriber S5 can only select the second modem M2, while the sixthsubscriber S6 also can select the second modem M3.

This means that if the third subscriber S3 is connected to the secondmodem M2, then if also the fourth subscriber S4 wants to be connected toa modem this cannot be done, but must be solved manually. On the otherhand if the third subscriber S3 is connected to the third modem M3, thenif also either the second subscriber S2 or the fifth subscriber S5 wantsto be connected to a modem this cannot be done, but must be solvedmanually. Since it is a higher probability that there will be a problemlater on if the third modem M3 is selected for the third subscriber S3,it is thus better so select the second modem M2 for the third subscriberS3.

In this way the number of relays can be reduced and thus money saved.Naturally this algorithm can be used in all contexts where many has toselect from a few items.

In FIG. 19 d it is shown how this can be implemented in thecross-connect.

The cross-connect can also be accomplished by using a multi-stepcross-connect, of which an example is shown in FIG. 22. First there is aseries of sixty-eight small first switch-matrixes 151, each with threeinputs and three outputs to a total of 204 inputs and outputs. The threeoutputs of the first switch-matrixes 151 are each connected to one ofthree second switch-matrixes 152, which thus have sixty-eight inputseach. The second switch-matrixes 152 then concentrate the connections byhaving only ten outputs each. The ten outputs of each secondswitch-matrix are then each connected to one of ten thirdswitch-matrixes 153, which thus have three inputs each. The thirdswitch-matrixes 153 then concentrate the connections by having only twooutputs each. Thus, totally the multi-step cross-connect in FIG. 21 has204 inputs and 20 outputs. This may naturally be varied in numerous wayswithout departing from the idea.

It can be shown that further relays can be saved with thisconfiguration. However, to make the most efficient multi-stepcross-connect, normal relays should also be included, especially insecond switch-matrixes 152, to enable certain reconfigurations of theconnections to be made.

In the description above, the cross-connect has consequently been usedto select xDSL modems for telecom subscribers. The skilled man in theart will however easily see that the cross-connect can be used also inother contexts where a choice is to be in principle non-reversible. Thisapplies in particular when a few outputs can be chosen by many inputs.

1. A method for connecting one of several first items to one of severalsecond items, wherein the first items and the second items are connectedto a cross-connect including switching columns, switching rows,addressing columns, addressing rows and fuse-relays: said methodcomprising the steps of: selecting a second item to which a selectedfirst item is to be connected; addressing an addressing column and anaddressing row in the cross-connect; and transmitting a high currentthrough said addressing row and addressing column sufficient to blow afuse in one of the fuse-relays whereby a connection is caused to be madeor broken between a switching row and a switching column, therebyconnecting the selected first item with the selected second item;wherein the first items are terminals and the second items are xDSLmodems.
 2. A method according to claim 1, wherein the cross-connectfurther includes additional switching rows, and a connection is causedto be made or broken between a switching row and an additional switchingrow when the fuse is blown.
 3. A method according to claim 1, furthercomprising the step of selecting the second item where the rest of thefirst items able to connect to said second item either already areconnected to another second item or have the highest possibility to beconnected to another second item.